K390 Steel: Edge Retention vs. Corrosion Care

Knife steel is only one of the things you’re liable to love about premium knives like Spyderco knives, but all the same, some of them are made in variants with some unique alloys, such as K390. 

This alloy sports a fairly unique mix of constituent elements and is one of the more wear-resistant steels out there right now, but that’s not all it offers. Let’s take a closer look.

What Is K390 Steel?

K390 is a steel alloy that’s produced by Bӧhler-Uddeholm, which is why it is sometimes referred to as Bӧhler K390. It was developed as an alternative to CPM-10V, which was renowned for its hardness and toughness, two attributes that are not always encountered in a single knife steel. This is because as hardness increases, brittleness tends to follow. As a result, some of the hardest alloys out there are also considered wanting in toughness, and conversely, some very tough steels are relatively soft. This is not always the case but it is common enough. 

That being said, one of the keys to K390’s performance as a hard, wear-resistant steel alloy that will hold an edge for a long time is the fact that it is rich in both carbon and in carbide-forming elements. Together the concentration of carbon and carbides result in a steel that is very hard. 

But to say K390 has a lot of carbon would be an understatement. It has nearly three times as much as other common tool steels, like 1095, have; it has 2.47% in its matrix. That concentration of carbon alone would render this steel capable of taking a heat treatment that would yield a long-lasting edge, but that’s to say nothing of the carbide-forming elements that are also present in this steel, and in high concentrations. 

What K390 also packs are cobalt, tungsten, and vanadium, the latter in a ridiculously high concentration. It sports 2% cobalt, 1% tungsten, and a whopping 9% of vanadium. All three of these elements form carbides with carbon, which are extremely hard compounds that increase hardness, wear-resistance, and edge retention. 

In the case of vanadium, this is pronounced. K390’s carbide composition is rich and dense, which is the other half of the picture here. It is an exceptionally hard steel that can take an edge that will last a long time. The one catch is that with this high hardness comes a commensurate difficulty in sharpening. 

Yes, you will be able to get a very sharp edge with K390 and it will hold it for a long time; but the tradeoff is that you will need a lot of patience when it comes time to resharpen the knife. It will be a labor of love.

The other cool thing about K390 is that it has 3.8% of molybdenum, an element that, among other things, increases the general toughness of a steel alloy that contains it. The same goes for tungsten; even though tungsten forms carbides, it also makes the steel that bears it very tough, as a general rule. 

So, to wrap this up, the main two attributes you get from K390 are that it is very hard (so it holds an edge for a long time) and it is fairly tough. 

There is, however, one big drawback. Partially as a result of the low concentration of chromium (it only has 4.2%) this is not considered a stainless steel. 

So, how can you keep Spyderco knives made with it from rusting?

Keeping Rust Off Your Spyderco Knives (and Some Basic Maintenance) 

Keeping rust off a Spyderco knife made with K390 steel starts with prevention. Here are some high level notes: 

• Avoid exposing your knife to marine environments.
• Don’t allow your knife to be submerged in water, as it will be hard to thoroughly dry it out afterwards and trapped moisture will result in corrosion. 
• Do not store your knives made with non-stainless alloys in high-humidity environments. 
• Always thoroughly clean and dry the blade before folding and storing the knife. 
• Periodically treat the knife with an appropriate oil, like tsubaki oil, before storing it. A drop, evenly distributed on both sides of the blade, should do it.
• You can also use compressed air to blast out moisture and dust from the area between the knife frame/scales.

At the end of the day, K390 is a great steel and a slightly lower resistance to corrosion is a small price to pay for a steel that is so hard and so tough. You just need to be a little more conscientious about how you handle, clean, and store your knives. 

Explore Spyderco Knives Here

In the market for Spyderco knives made with steels like the one mentioned here? Check out our full collection and whether you’re looking for a Spydie in K390 or would prefer a slightly more corrosion resistant model, let us know. We are more than happy to make a personalized recommendation.